As an image display device substitutable for liquid crystal display (LCD), image display devices with the use of technology such as an electrophoresis method, an electro-chromic method, a thermal method, dichroic-particles-rotary method are proposed.
As for these image display device, it is conceivable as inexpensive visual display device of the next generation from a merit having wide field of vision close to normal printed matter, having smaller consumption with LCD, spreading out to a display for portable device, and an electronic paper is expected. Recently, electrophoresis method is proposed that microencapsulate dispersion liquid made up with dispersion particles and coloration solution and dispose the liquid between faced substrates.
However, in the electrophoresis method, there is a problem that a response speed is slow by the reason of viscosity resistance because the particles migrate among the electrophoresis solution. Further, there is a problem of lacking imaging repetition stability, because particles with high specific gravity of titanium oxide is scattered within solution of low specific gravity, it is easy to subside, difficult to maintain a stability of dispersion state. Even in the case of microencapsulating, cell size is diminished to a microcapsule level in order to make it hard to appear, however, an essential problem was not overcome at all.
Besides the electrophoresis method using behavior in the solution, recently, a method wherein electroconductive particles and a charge transport layer are installed in a part of the substrate without using solution is proposed. However, the structure becomes complicated because the charge transport layer and further a charge generation layer are to be arranged. In addition, it is difficult to constantly dissipate charges from the electro-conductive particles, and thus there is a drawback on the lack of stability.
As one method for overcoming the various problems mentioned above, an image display device comprising an image display panel is known, in which two or more groups of particles having different colors and different charge characteristics are sealed between two substrates, at least one of two substrates being transparent, and, in which the particles, to which an electrostatic field produced by a pair of electrodes provided on respective substrates is applied, are made to fly and move so as to display an image by means of Coulomb's force.
Tasks to be solved by a first aspect of the invention are as follows. That is, the image display device mentioned above has a display memory property (keeping display even after power OFF). In the case of the image display device having such display memory property, it is necessary to form one image by alternately changing an electric field direction Ea (polarity) in which particles A are flown toward a display substrate and an electric field direction Eb in which particles B having different colors and different charge characteristics as those of the particles A are flown toward the display substrate. That is, in the case that an image-1 formed by the particles A and the particles B is rewritten to an image-2 formed also by the particles A and the particles B, if the image-2 is rewritten only by Ea, only a portion at which the particles A are flown to the display panel by Ea is rewritten, and a portion which is rewritable by the particles B is not changed.
Therefore, as shown in FIG. 15, it is thought one method wherein the image is formed in such a manner that an image deleting step is performed prior to an image forming step (the image is formed only by the particles A or the particles B) and then the image forming step is performed by using the electric field direction different from the electric field direction using at the image deleting step. However, in the case of matrix display for example, as shown in FIG. 16, if the image deleting step is performed at a front line of a frame time, a portion wherein the image is formed first in the frame time (line) and a portion wherein the image is formed last in the frame time (line) have a different time duration from one image deleting step to the next image deleting step. Therefore, there is a drawback such that density unevenness occurs in the image and a display quality is extremely deteriorated.
Tasks to be solved by a second aspect of the invention are as follows. That is, the image display device mentioned above has a display memory property (keeping display even after power OFF). In the case of the image display device having such display memory property, it is necessary to form one image by alternately changing an electric field direction Ea (polarity) in which particles A are flown toward a display substrate and an electric field direction Eb in which particles B having different colors and different charge characteristics as those of the particles A are flown toward the display substrate. Therefore, in the case of displaying a halftone image by this image display device, it is possible to obtain a halftone image by adjusting a display time ratio of particle A/particle B during the interval such that the particle A/particle B is repeated by applying the electric fields Ea and Eb at a frequency where flickering is not detected by a human eye. However, the halftone image display according to the method mentioned above has a drawback such that the image memory property cannot be obtained.
Tasks to be solved by a third aspect of the invention are as follows. That is, the image display device mentioned above has a display memory property (keeping display even after power OFF). In the case of the image display device having such display memory property, it is necessary to form one image by alternately changing an electric field direction Ea (polarity) in which particles A are flown toward a display substrate and an electric field direction Eb in which particles B having different colors and different charge characteristics as those of the particles A are flown toward the display substrate. In the image display device mentioned above, the halftone image display is performed by displaying repeatedly the particle A/particle B at a frequency where flickering is not detected by a human eye and changing a ratio thereof. However, the halftone image display according to the method mentioned above has a drawback such that the image memory property cannot be obtained.
Tasks to be solved by a fourth aspect of the invention are as follows. That is, the image display device mentioned above has a display memory property (keeping display even after power OFF). In the case of the image display device having such display memory property, it is necessary to form one image by alternately changing an electric field direction Ea (polarity) in which particles A are flown toward a display substrate and an electric field direction Eb in which particles B having different colors and different charge characteristics as those of the particles A are flown toward the display substrate. Therefore, in the case of displaying a halftone image by this image display device, it is possible to obtain a halftone image by adjusting a display time ratio of particle A/particle B during when the particle A/particle B is repeated by applying the electric fields Ea/Eb. However, the halftone image display according to the method mentioned above has a drawback such that a driving circuit of image display elements becomes complicated.
Tasks to be solved by a fifth aspect of the invention are as follows. That is, the image display device mentioned above is assumed to perform a binary display from a microscopic view, but the halftone display due to respective pixels is accomplished by maintaining an intermediate state such that particle characteristics are intentionally deviated and a part of particles which are easily flown is only moved.
However, the halftone image display according to the method mentioned above has a drawback such that an excellent reproducibility of the halftone image display cannot be performed since resistivity and so on of ITO transparent electrode is deviated, an electrode surface is contaminated by a particle component, and a threshold voltage when the particles are moved from the electrode surface due to a throw off force larger than an adhesion force. Therefore, especially in the case of performing the matrix drive that needs a precipitous threshold, the number of gray scales that can be displayed is limited.